The present invention is directed to intercalated layered materials, and exfoliates thereof, manufactured by sorption (adsorption and/or absorption) of one or more functional monomeric organic compounds between planar layers of a swellable layered material, such as a phyllosilicate or other layered material, to expand the interlayer spacing of adjacent layers to at least about 5 Angstroms (xc3x85), preferably at least about 10 xc3x85. More particularly, the present invention is directed to intercalates having at least two layers of monomeric organic compounds sorbed on the internal surfaces of adjacent layers of the planar platelets of a layered material, such as a phyllosilicate, preferably a smectite clay, to expand the interlayer spacing to at least about 5 xc3x85, preferably at least about 10 xc3x85, more preferably to at least about 20 xc3x85, and most preferably to at least about 30-45 xc3x85, up to about 100 xc3x85, or disappearance of periodicity. The intercalated layered materials preferably have at least two layers of monomeric hydroxyl-functional, polyhydroxyl-functional, or aromatic-functional molecules sorbed on the internal surfaces between adjacent layers of the planar platelets of the layered material, such as a phyllosilicate, preferably a smectite clay. The resulting intercalates are neither entirely organophilic nor entirely hydrophilic, but a combination of the two, and easily can be exfoliated and combined as individual platelets with a polar organic solvent carrier to form a viscous composition having a myriad of uses. The resulting polar organic solvent carrier/intercalate or carrier/platelet composite materials are useful as plasticizers; for providing increased viscosity and elasticity to thermoplastic and thermosetting polymers, e.g., for plasticizing polyvinyl chloride; for food wrap having improved gas impermeability; electrical components; food grade drink containers; particularly for raising the viscosity of polar organic liquids; and for altering one or more physical properties of a matrix polymer, such as elasticity and temperature characteristics, e.g., glass transition temperature and high temperature resistance.
It is well known that phyllosilicates, such as smectite clays, e.g., sodium montmorillonite and calcium montmorillonite, can be treated with organic molecules, such as organic ammonium ions, to intercalate the organic molecules between adjacent, planar silicate layers, for bonding the organic molecules with a polymer, for intercalation of the polymer between the layers, thereby substantially increasing the interlayer (interlaminar) spacing between the adjacent silicate layers. The thus-treated, intercalated phyllosilicates, having interlayer spacings of at least about 10-20 xc3x85 and up to about 100 Angstroms, then can be exfoliated, e.g., the silicate layers are separated, e.g., mechanically, by high shear mixing. The individual silicate layers, when admixed with a matrix polymer, before, after or during the polymerization of the matrix polymer, e.g., a polyamidexe2x80x94see U.S. Pat. Nos. 4,739,007; 4,810,734; and 5,385,776 xe2x80x94have been found to substantially improve one or more properties of the polymer, such as mechanical strength and/or high temperature characteristics.
Exemplary prior art composites, also called xe2x80x9cnanocompositesxe2x80x9d, are disclosed in published PCT disclosure of Allied Signal, Inc. WO 93/04118 and U.S. Pat. No. 5,385,776, disclosing the admixture of individual platelet particles derived from intercalated layered silicate materials, with a polymer to form a polymer matrix having one or more properties of the matrix polymer improved by the addition of the exfoliated intercalate. As disclosed in WO 93/04118, the intercalate is formed (the interlayer spacing between adjacent silicate platelets is increased) by adsorption of a silane coupling agent or an onium cation, such as a quaternary ammonium compound, having a reactive group which is compatible with the matrix polymer. Such quaternary ammonium cations are well known to convert a highly hydrophilic clay, such as sodium or calcium montmorillonite, into an organophilic clay capable of sorbing organic molecules. A publication that discloses direct intercalation (without solvent) of polystyrene and poly(ethylene oxide) in organically modified silicates is Synthesis and Properties of Two-Dimensional Nanostructures by Direct Intercalation of Polymer Melts in Layered Silicates, Richard A. Vaia, et al., Chem. Mater., 5:1694-1696(1993). Also as disclosed in Adv. Materials, 7, No. 2: (1985), pp, 154-156, New Polymer Electrolyte Nanocomposites: Melt Intercalation of Poly(Ethylene Oxide) in Mica-Type Silicates, Richard A. Vaia, et al., poly(ethylene oxide) can be intercalated directly into Na-montmorillonite and Li-montmorillonite by heating to 80xc2x0 C. for 2-6 hours to achieve a d-spacing of 17.7 xc3x85. The intercalation is accompanied by displacing water molecules, disposed between the clay platelets, with polymer molecules. Apparently, however, the intercalated material could not be exfoliated and was tested in pellet form. It was quite surprising to one of the authors of these articles that exfoliated material could be manufactured in accordance with the present invention.
Previous attempts have been made to intercalate polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA) and poly(ethylene oxide) (PEO) between montmorillonite clay platelets with little success. As described in Levy, et al., Interlayer Adsorption of Polyvinylpyrrolidone on Montmorillonite, Journal of Colloid and Interface Science, Vol. 50, No. 3, March 1975, pages 442-450, attempts were made to sorb PVP (40,000 average M.W.) between monoionic montmorillonite clay platelets (Na, K, Ca and Mg) by successive washes with absolute ethanol, and then attempting to sorb the PVP by contact with 1% PVP/ethanol/water solutions, with varying amounts of water, via replacing the ethanol solvent molecules that were sorbed in washing (to expand the platelets to about 17.7 xc3x85). Only the sodium montmorillonite had expanded beyond a 20 xc3x85 basal spacing (e.g., 26 xc3x85 and 32 xc3x85), at 5+% H2O, after contact with the PVP/ethanol/H2O solution. It was concluded that the ethanol was needed to initially increase the basal spacing for later sorption of PVP, and that water did not directly affect the sorption of PVP between the clay platelets (Table II, page 445), except for sodium montmorillonite. The sorption was time consuming and difficult and met with little success.
Further, as described in Greenland, Adsorption of Polyvinyl Alcohols by Montmorillonite, Journal of Colloid Sciences, Vol. 18, pages 647-664 (1963), polyvinyl alcohols containing 12% residual acetyl groups could increase the basal spacing by only about 10 xc3x85 due to the sorbed polyvinyl alcohol (PVA). As the concentration of polymer in the intercalant polymer-containing solution was increased from 0.25% to 4%, the amount of polymer sorbed was substantially reduced, indicating that sorption might only be effective at polymer concentrations in the intercalant polymer-containing composition on the order of 1% by weight polymer, or less. Such a dilute process for intercalation of polymer into layered materials would be exceptionally costly in drying the intercalated layered materials for separation of intercalate from the polymer carrier, e.g., water, and, therefore, apparently no further work was accomplished toward commercialization.
In accordance with one embodiment of the present invention, intercalates are prepared by contacting a phyllosilicate with a monomeric organic compound having an electrostatic functionality selected from the group consisting of a hydroxyl; a polyhydroxyl; an aromatic functionality; and mixtures thereof.
In accordance with an important feature of the present invention, best results are achieved using the monomeric organic compound, having at least one of the above-defined functionalities, in a concentration of at least about 2%, preferably at least about 5% by weight functional monomeric organic compound, more preferably at least about 10% by weight monomeric organic compound, and most preferably about 30% to about 80% by weight, based on the weight of functional monomeric organic compound and carrier (e.g., water, with or without an organic solvent for the functional monomeric compound) to achieve better sorption of the functional monomeric organic compound between phyllosilicate platelets. Regardless of the concentration of functional monomeric organic compound in aqueous liquid, the intercalating composition should have a functional monomeric organic compound:layered material ratio of at least 1:20, preferably at least 1:10, more preferably at least 1:5, and most preferably about 1:4 to achieve efficient intercalation of the functional monomeric organic compound between adjacent platelets of the layered material. The functional monomeric organic compound sorbed between and bonded to the silicate platelets causes separation or added spacing between adjacent silicate platelets.
For simplicity of description, the above-described functional monomeric organic compounds are hereinafter called the xe2x80x9cintercalantxe2x80x9d or xe2x80x9cintercalant monomerxe2x80x9d or xe2x80x9cmonomer intercalantxe2x80x9d. The monomer intercalant will be sorbed sufficiently to increase the interlayer spacing of the phyllosilicate in the range of about 5 xc3x85 to about 100 xc3x85, preferably at least about 10 xc3x85 for easier and more complete exfoliation, in a commercially viable process, regardless of the particular phyllosilicate or intercalant monomer.
In accordance with the present invention, it has been found that a phyllosilicate, such as a smectite clay, can be intercalated sufficiently for subsequent exfoliation by sorption of organic monomer compounds that have a hydroxyl or polyhydroxyl functionality; or at least one aromatic ring to provide bonding between two functional hydroxyl groups of one or two intercalant monomer molecules and the metal cations of the inner surfaces of the phyllosilicate platelets. Sorption and metal cation attraction or bonding of a platelet metal cation between two hydroxyl groups of the intercalant monomer molecules; or the bonding between the interlayer cations in hexagonal or pseudohexagonal rings of the smectite platelet layers and an intercalant monomer aromatic ring structure, is provided by a mechanism selected from the group consisting of ionic complexing; electrostatic complexing; chelation; hydrogen bonding; dipole/dipole; Van Der Waals forces; and any combination thereof.
Such bonding, via a metal cation of the phyllosilicate sharing electrons with two electronegative atoms of one or two intercalant monomer molecules, to an inner surface of the phyllosilicate platelets provides adherence between the functional monomeric organic molecules and the platelet inner surfaces of the layered material, and increases the interlayer spacing between adjacent silicate platelets or other layered material to at least about 5 xc3x85, preferably to at least about 10 xc3x85, more preferably to at least about 20 xc3x85, and most preferably in the range of about 30 xc3x85 to about 45 xc3x85. The electronegative atoms can be, for example, oxygen, sulfur, nitrogen, and combinations thereof.
Such intercalated phyllosilicates easily can be exfoliated into individual phyllosilicate platelets before or during admixture with a liquid carrier or solvent, for example, one or more monohydric alcohols, such as methanol, ethanol, propanol, and/or butanol; polyhydric alcohols, such as glycerols and glycols, e.g., ethylene glycol, propylene glycol, butylene glycol, glycerine and mixtures thereof; aldehydes; ketones; carboxylic acids; amines; amides; and other organic solvents, for delivery of the solvent in a thixotropic composition, or for delivery of any active hydrophobic or hydrophilic organic compound, such as a topically active pharmaceutical, dissolved or dispersed in the carrier or solvent, in a thixotropic composition; or the intercalates and/or exfoliates thereof can be admixed with a polymer or other organic monomer compounds or composition to increase the viscosity of the organic compound or provide a polymer/intercalate and/or exfoliate composition to enhance one or more properties of a matrix polymer.
Whenever used in this Specification, the terms set forth shall have the following meanings:
xe2x80x9cLayered Materialxe2x80x9d shall mean an inorganic material, such as a smectite clay mineral, that is in the form of a plurality of adjacent, bound layers and has a thickness, for each layer, of about 3 xc3x85 to about 50 xc3x85, preferably about 10 xc3x85.
xe2x80x9cPlateletsxe2x80x9d shall mean individual layers of the Layered Material.
xe2x80x9cIntercalatexe2x80x9d or xe2x80x9cIntercalatedxe2x80x9d shall mean a Layered Material that includes hydroxyl-functional organic monomer molecules and/or aromatic-functional organic monomer molecules disposed between adjacent platelets of the Layered Material to increase the interlayer spacing between the adjacent platelets to at least about 5 xc3x85, preferably at least about 10 xc3x85.
xe2x80x9cIntercalationxe2x80x9d shall mean a process for forming an Intercalate.
xe2x80x9cIntercalant Monomerxe2x80x9d or xe2x80x9cIntercalantxe2x80x9d shall mean a monomeric organic compound that includes a functionality selected from the group consisting of a hydroxyl; a polyhydroxyl; an aromatic ring; and mixtures thereof that is sorbed between Platelets of the Layered Material and complexes with the platelet surfaces to form an Intercalate.
xe2x80x9cIntercalating Carrierxe2x80x9d shall mean a carrier comprising water with or without an organic solvent used together with an Intercalant Monomer to form an Intercalating Composition capable of achieving Intercalation of the Layered Material.
xe2x80x9cIntercalating Compositionxe2x80x9d shall mean a composition comprising an Intercalant Monomer, an Intercalating Carrier for the Intercalant Monomer, and a Layered Material.
xe2x80x9cExfoliatexe2x80x9d or xe2x80x9cExfoliatedxe2x80x9d shall mean individual platelets of an Intercalated Layered Material so that adjacent platelets of the Intercalated Layered Material can be dispersed individually throughout a carrier material, such as water, a polymer, an alcohol or glycol, or any other organic solvent.
xe2x80x9cExfoliationxe2x80x9d shall mean a process for forming an Exfoliate from an Intercalate.
In brief, the present invention is directed to intercalates and exfoliates thereof formed by contacting a layered phyllosilicate with a functional organic monomer (intercalant monomer), having at least one hydroxyl functionality and/or an aromatic ring, to sorb or intercalate the intercalant monomer or mixtures of intercalant monomers between adjacent phyllosilicate platelets. Sufficient intercalant monomer is sorbed between adjacent phyllosilicate platelets to expand the spacing between adjacent platelets (interlayer spacing) to a distance of at least about 5 xc3x85, preferably to at least about 10 xc3x85 (as measured after water removal to a maximum water content of 5% by weight, based on the dry weight of the layered material) and more preferably in the range of about 30-45 xc3x85, so that the intercalate easily can be exfoliated, sometimes naturally without shearing being necessary. At times, the intercalate requires shearing that easily can be accomplished, e.g., when mixing the intercalate with a polar organic solvent carrier, such as a polar organic hydrocarbon, and/or with a polymer melt to provide a platelet-containing composite material or nanocompositexe2x80x94the platelets being obtained by exfoliation of the intercalated phyllosilicate.
The intercalant monomer has an affinity for the phyllosilicate so that it is sorbed between, and is maintained associated with the silicate platelets in the interlayer spaces, and after exfoliation. In accordance with the present invention, the intercalant monomer should include an aromatic ring and/or have a hydroxyl or polyhydroxyl functionality to be sufficiently bound, it is hereby theorized, by a mechanism selected from the group consisting of ionic complexing; electrostatic complexing; chelation; hydrogen bonding; dipole/dipole; Van Der Waals forces; and any combination thereof. Such bonding, via a metal cation of the phyllosilicate sharing electrons with electronegative atoms of one or two hydroxyl or aromatic ring structures, to an inner surface of the phyllosilicate platelets provides adherence between the intercalant monomer molecules and the platelet inner surfaces of the layered material. The electronegative atoms can be, for example, oxygen, sulfur, nitrogen, and combinations thereof. Atoms having a sufficient electronegativity to bond to metal cations on the inner surface of the platelets have an electronegativity of at least 2.0, and preferably at least 2.5, on the Pauling Scale. A xe2x80x9cpolar moietyxe2x80x9d or xe2x80x9cpolar groupxe2x80x9d is defined as a moiety having two adjacent atoms that are bonded covalently and have a difference in electronegativity of at least 0.5 electronegativity units on the Pauling Scale.
Such intercalant monomers have sufficient affinity for the phyllosilicate platelets to maintain sufficient interlayer spacing for exfoliation, without the need for coupling agents or spacing agents, such as the onium ion or silane coupling agents disclosed in the above-mentioned prior art. A schematic representation of the charge distribution on the surfaces of a sodium montmorillonite clay is shown in FIGS. 1-3. As shown in FIGS. 2 and 3, the location of surface Na+cations with respect to the location of oxygen (Ox), Mg, Si and Al atoms (FIGS. 1 and 2) results in a clay surface charge distribution as schematically shown in FIG. 3. The positive-negative charge distribution over the entire clay surface provides for excellent dipole/dipole attraction of polar hydroxyl-functional and/or aromatic-functional monomers on the surfaces of the clay platelets.
The intercalate-containing and/or exfoliate containing compositions can be in the form of a stable thixotropic gel that is not subject to phase separation and can be used to deliver any active materials, such as in the cosmetic, hair care and pharmaceutical industries. The layered material is intercalated and optionally exfoliated by contact with an intercalant monomer and water and then mixed and/or extruded to intercalate the monomer between adjacent phyllosilicate platelets and optionally separate (exfoliate) the layered material into individual platelets. The amount of water varies, depending upon the amount of shear imparted to the layered material in contact with the intercalant monomer and water. In one method, the intercalating composition is pug milled or extruded at a water content of about 25% by weight to about 50% by weight water, preferably about 35% to about 40% by weight water, based on the dry weight of the layered material, e.g., clay. In another method, the clay and water are slurried, with at least about 25% by weight water, preferably at least about 65% by weight water, based on the dry weight of the layered material, e.g., preferably less than about 20% by weight clay in water, based on the total weight of layered material and water, more preferably less than about 10% layered material in water, with the addition of about 2% by weight to about 90% by weight intercalant monomer, based on the dry weight of the layered material.
Sorption of the intercalant monomer should be sufficient to achieve expansion of adjacent platelets of the layered material (when measured dry) to an interlayer spacing of at least about 5 xc3x85, preferably to a spacing of at least about 10 xc3x85, more preferably a spacing of at least about 20 xc3x85, and most preferably a spacing of about 30-45 xc3x85. To achieve intercalates that can be exfoliated easily using the monomer intercalants disclosed herein, the weight ratio of intercalant monomer to layered material, preferably a water swellable smectite clay such as sodium bentonite, in the intercalating composition should be at least about 1:20, preferably at least about 1:12 to 1:10, more preferably at least about 1:5, and most preferably about 1:5 to about 1:3. It is preferred that the concentration of intercalant monomer in the intercalating composition, based on the total weight of intercalant monomer plus intercalant carrier (water plus any non-hydroxyl-containing and non-aromatic ring-containing organic liquid solvent) in the intercalating composition is at least about 15% by weight, more preferably at least about 20% by weight intercalant monomer, for example about 20-30% to about 90% by weight intercalant monomer, based on the weight of intercalant monomer plus intercalating carrier in the intercalant composition during intercalation.
Interlayer spacings sufficient for exfoliation have never been achieved by direct intercalation of the above-defined intercalant monomers, without prior sorption of an onium or silane coupling agent, and provides easier and more complete exfoliation for or during incorporation of the platelets into a polar organic compound or a polar organic compound-containing composition carrier or solvent to provide unexpectedly viscous carrier compositions, for delivery of the carrier or solvent, or for administration of an active compound that is dissolved or dispersed in the carrier or solvent. Such compositions, especially the high viscosity gels, are particularly useful for delivery of active compounds, such as oxidizing agents for hair waving lotions, and drugs for topical administration, since extremely high viscosities are obtainable; and for admixtures of the platelets with polar solvents in modifying rheology, e.g., of cosmetics, oil-well drilling fluids, paints, lubricants, especially food grade lubricants, in the manufacture of oil and grease, and the like. Such intercalates also are especially useful in admixture with matrix thermoplastic or thermosetting polymers in the manufacture of polymeric articles from the polar organic carrier/polymer/intercalate and/or platelet composite materials.
Once exfoliated, the platelets of the intercalate are predominantly completely separated into individual platelets and the originally adjacent platelets no longer are retained in a parallel, spaced disposition, but are free to move as predominantly individual intercalant monomer-coated (continuously or discontinuously) platelets throughout a carrier or solvent material to maintain viscosity and thixotropy of the carrier material. The predominantly individual phyllosilicate platelets, having their platelet surfaces complexed with intercalant monomer molecules, are randomly, homogeneously and uniformly dispersed, predominantly as individual platelets, throughout the carrier or solvent to achieve new and unexpected viscosities in the carrier/platelet compositions even after addition of an active organic compound, such as a cosmetic component or a medicament, for administration of the active organic compound (s) from the composition.
As recognized, the thickness of the exfoliated, individual platelets (about 10 xc3x85) is relatively small compared to the size of the flat opposite platelet faces. The platelets have an aspect ratio in the range of about 200 to about 2,000. Dispersing such finely divided platelet particles into a polymer melt or into a polar organic liquid carrier imparts a very large area of contact between carrier and platelet particles, for a given volume of particles in the composite, and a high degree of platelet homogeneity in the composite material. Platelet particles of high strength and modulus, dispersed at sub-micron size (nanoscale), impart greater mechanical reinforcement and a higher viscosity to a polar organic liquid carrier than do comparable loadings of conventional reinforcing fillers of micron size, and can impart lower permeability to matrix polymers than do comparable loadings of conventional fillers.